text:
What is the reason for the sudden increase of French published accident and incident investigation reports in 1997?
The number of accidents and incident reports available online at BEA has changed dramatically between 1996 and 1997:

There was an average of 2 reports per year until 1996, and an average of about 125 reports per year then.
As it is unlikely that there was a sudden increase in the number of events, something in the French legislation and/or the policy of BEA must have changed.
What was the actual reason for this change and sudden increase?

This is total guesswork, but it could it be that around 1996 the reports were digitized, and thus all are available online, but reports prior to 1996 must be converted to digital format?

That seems to make sense,  but it would be very odd to digitize only very few of the old reports, instead of all or none.

I wonder if your collection is accurate. E.g. in your graphic, there is no report in 74 nor 76. But actually I found the BEA investigated the tragic accident involving Turkish Airlines TC-JAV which occurred in Ermenonville in France in 74. The report was published in 76 on the "JO de la République" which is the legal publication for State decisions and laws (and is indeed public). A pdf file is available on BEA site. Article on Wikipedia.

@mins It is related to investigation reports. There is a separate category for notified events, which have very similar numbers with a very similar sudden increase from 1996 to 1997. Your note about 1974 is correct, there is one record that I missed. The graph is updated.

@mins see updated graph. Starting from 2008 the reports may be filtered by type, but it doesn't work for the older ones. The majority are accident reports. Interim reports are included. Note that for your example on F-GZCP the interim report is also the only report available.

There were 3 interim reports and a final report. All can be accessed here ("Download" in the top right corner). I really doubt your count is complete, not a criticism, but there is no possibility to check.

@mins I see. The 3 interim plus the final report are counted as one report. For your case, the search result is the one that you have linked. I really do not understand why you distrust the count. It is very simple.

@mins about the colours: do you imply that there should be more incidents than accidents? Sorry, this is the data the BEA site delivered. It is not swapped.

1996 is certainly a very plausible date for beginning "born-digital" records. It's also possible they're doing them retroactively in batches (with a few special cases done out of sequence, perhaps when they were digitised for other reasons) and just haven't got back earlier than 1996 yet...

@Andrew: While the internet was still in its first years, local network, email and text processing were already well common in enterprises and administrations for at least 5 years, and laptop was starting to spread. I can't imagine the BEA using paper for their reports after 1990.

A related event could be the adoption by The European Community Council of:

Council Directive 94/56/EC of 21 November 1994 establishing the fundamental principles governing the investigation of civil aviation accidents and incidents [Official Journal L 319 of 12.12.1994].

European directives must be transposed in a country law and adopted by the country Parliament. This has been done for France in 1999, with the law "Loi n°99-243 du 29 mars 1999". This law actually modified the regulations related to civil aviation (Code de l'Aviation Civile, Livre VII).
Most of the articles added new obligations to the State and, from what I understand, no obligation for investigation or for releasing a public report existed before, so it may have been at the discretion of the Transport Ministry.
Two articles are of interest:

Obligation to investigate every accident or serious incident with the
  aim of preventing any reoccurrence thereof.

and

Obligation to publish an accident (or incident) report, containing
  safety recommendations where appropriate.

Regarding your count on the BEA site, this info is lacking some important details, for instance:

The hang-glider or ultralight aircraft are relatively new, and we don't know how it has changed the number of incidents/accidents. It's well known that in France hang-glider accidents where not investigated by the BEA because hang-gliders are not subject to an airworthiness certificate. It seems this has changed, but it's not clear to me.
You don't provide a list of events, only a list of reports, which as demonstrated in the Rio-Paris accident can multiply by 4 the count because of the 3 interim reports (this is now mandatory to publish a preliminary report each 12 months if the final report cannot be completed within the first year).

It seems quite clear that this is a digitization artifact. Remember that the internet hasn't been around forever, and making old reports available doesn't just mean copying the PDF to the right place on the webserver because PDF didn't even exist before 1993.

Word processing was already daily used by enterprises and organizations in 1995 (e.g. Word 95). Batch converting .doc to .pdf is not big deal. Indeed those electronic documents were not published online like today.

The transition from scanned to digital-borne BEA reports takes place from 1991 to 1993.


text:
Which official document lists active airport identifiers?
Is there an official FAA document with which I can find an airport by its identifier code if I do not have a name or location? In the Chart Supplement I can find the airport if I know the city and state. However, I can’t seem to find any sort of reverse lookup document that lets me find it by code only.
I know I can search on SkyVector/ForeFlight/etc. but I am specifically asking if there is a government published “index document” for this.

Digital Aeronautical Flight Information File
This database, commonly just called "DAFIF", is maintained by the National Geospatial-Intelligence Agency (NGA). Unfortunately, updates to this database are no longer published to public domain as of 2006. If you are not an authorized user, you can still use pre-2006 data from sources around the internet, which will likely be good enough for what you need. Look around for "DAFIF cycle 0610". The database contains ARPT.TXT, a tab-separated text file with metadata for both large and small airports around the world, including various types of identifiers (ICAO, FAA-ID, Name, Lat/Lon, etc).
https://en.wikipedia.org/wiki/DAFIF

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text:
Could an airliner exceed Mach 1 in a zero-G power dive and safely recover?
(I looked for duplicates. I really did.)
Being as it is that "safety" and this are mutually exclusive:
I am stupid. I take a cruising A320, apply TOGA power, and push zero Gs until I exceed Mach 1. How do I get out of this in one piece? And how much faster can I go before I need to start this process of getting out in one piece?

You survive by being really careful to not over-G the jet!

I have not been able to find the article, but I live in Wichita, and during development of the Cessna Citation X there was a modified nose cone which permitted supersonic flight.  It was experimental, and developing it was not cost efficient, but it was done and the airframe handled it with little difficulty.  If I find the link I'll post it.

@J... That applies if you panic, pull back too hard and end up doing 9Gs for no reason.

There is a good question in there somewhere, as evidenced by some really good answers.  I wouldn't have known about the DC-8 test otherwise.  Something along the lines of "what mach number are typical jet airliners normally designed to safely recover from during an upset?"  Or conversely "has any modern jet airliner been intentionally tested above mach 1.0 to ensure safe recovery was possible?"  Or maybe, "at what mach number might an airliner break up in flight due to aerodynamic flutter?"  But admitting your stupidity and asking how long you can wait to recover just invites criticism.

What's a "zero-G power dive" in which you push zero Gs until (anything) please? I can see a "zero-G dive" as one unpowered but then what?

@RobbieGoodwin: They mean specifically zero vertical (from the aircraft's point of view) Gs; i.e., flying the jet in a parabolic dive.  They will of course be experiencing nonzero longitudinal Gs as the engines help to accelerate the aircraft.

@Vikki Thanks and I don't see it. If it's in a dive, it's experiencing at least the 1G due to - uh - gravity. If Zero G means 'without engine power' that's a different thing, isn't it?

@RobbieGoodwin At any point of the dive assuming no power from the aircraft, you are being accelerated by the earth at 1G. If you Accelerate into that dive then with regards to the the aircraft there is 0G on the air frame and the contents, This is how the Vomit Comet works. Air frames are certified for a certain level of positive and negative G.

Thanks and no such details lead me to believe there's any more reason to suppose an airliner of unspecified characteristics might survive - or not - any given dive.
What am I missing/

There is actually some data (albeit limited) on this scenario:
On August 21st 1961 this test was performed in a DC-8. When this test was performed they were supersonic for about 16 seconds which took a lot of planning to pull off. You first need to climb higher than the plane typically does to have enough altitude to pull this off, then make sure you understand how the control surfaces are loaded in the dive. You get out in once piece by planning for it and understanding exactly what's going on:

We took it up to 10 miles up, 52,000 feet—that’s a record—and put it
in a half-a-G pushover. Bill maintained about 50 pounds of push. He
didn’t trim it for the dive so that it would want to pull out by
itself. In the dive, at about 45,000 feet, it went to Mach 1.01 for
maybe 16 seconds, then he recovered. But the recovery was a little
scary. When he pulled back, the elevator was ineffective; it didn’t do
anything, so he said, “Well, I’ll use the stabilizer,” and the
stabilizer wouldn’t run. It stalled, because of the load. What he did,
because he was smart, is something that no other pilot would do: He
pushed over into the dive more, which relieved the load on the
stabilizer. He was able to run the [stabilizer] motor, with the
relieved load, and he recovered at about 35,000 feet.

Remember you're diving fast, really fast, so you likely can't go much faster as you will ultimately run out of time to accelerate:

The Mach number itself isn’t used in a dive as a target because it’s
much more accurate to use airspeed. So every thousand feet I would
read off to Bill the airspeed [he needed] at the next altitude. As we
were coming down, I was talking almost all the time because at a
descent rate of 500 feet per second, every two seconds we were 1,000
feet lower. Looking out the window—which I stopped doing—it looked
like it was straight down.

The trick is to not over stress the airframe.

What, if any effect would throttling back had had?

@DigitalDracula From the B737 NG training manual, 2005: "Excessive airloads on the stabilizer may require effort by both pilots to correct the mis-trim. In extreme cases it may be necessary to aerodynamically relieve the airloads to allow manual trimming. Accelerate or decelerate towards the in-trim speed while attempting to trim manually." Rollercoaster or yo-yo.

That it was successful once was a science experiment. There is no guarantee that repeating this experiment will have the same result. Engineering is what is required to ensure reliable and repeatable operations. The A320 is not engineered to exceed M0.93. There can be no guarantees about survivability or repeatability of aircraft performance when operating outside of the absolute engineering limits. It might work out ok, it might not.

A descent rate of 500 doesn’t seem that bad. Oh wait, that’s per second, not per minute? Pointed straight at the ground indeed!

A couple of points for completeness: 1) The article mentions a 1/2g pushover, and I would guess that the subsequent acceleration was somewhere between that and1g; zero g in a near-vertical dive would imply a thrust equal to the drag at that speed, and if this airplane had that much thrust, it could have gone supersonic in level flight (without afterburners!) 2) The quoted passage about the recovery suggests that not everything about the flight had been anticipated and prepared for, but the test pilot's knowledge, skill and sang-froid brought about a successful conclusion.

@DigitalDracula Or, more precisely, it's like the way they could have recovered from the MAX issue. Pushing over to relieve load in order to be able to adjust the trim manually has always been in the 737 operating procedures in case of runaway trim where the powered actuator had to be disabled. The MCAS failure essentially was a runaway trim scenario, so it could be recovered just like any other runaway trim scenario.

@reirab That close to the ground, it is nearly impossible to convince yourself to push the nose down more. The only way that happens is if it is instinctive, an ingrained response through repetitive training. Same issue with engine failure on takeoff. No one in their right mind would push the nose down, yet that is exactly what is required.

@hemp You're right, but the pilots are supposed to be trained for runaway trim (just as with engine failure.)

The TWA Flight 841 accident in 1979 involving a Boeing 727 comes pretty close to your conditions. Not a zero-G dive but an unintended spiral dive starting at 39,000 feet, reaching mach 0.96 at 31,800 feet, becoming a 90 degree nose-down dive at 29,000 feet with total loss of control authority. With speed brakes ineffective, the pilot extended the landing gear in an attempt to slow the aircraft and finally regained control at about 5000 feet. The aircraft landed safely. Eight passengers received minor injuries, most of whom had been standing and were forced to the floor and held there by the 6-G acceleration force. The aircraft sustained damage, but it was repaired and returned to service.
Wikipedia
NTSB Report (PDF)

After you break the sound barrier, a shock wave will be generated in front of your main wings and tail wings. Though the design of wings on modern planes may hold that situation and can still generate some lift (which is impossible for traditional wings, leading to a fatal stall), the control surfaces on your main wings and tail wings will nearly lose their effect (the shock wave in front of the wing will weaken the energy of air flow near the control surface). So it will be extremely hard to pull up with normal control surfaces.
However, you do have other effective ways to control the plane. By adjusting the pitch trim, you can change the AOI of your tail wings, which is still effective in the supersonic situation and will be the main way for you to pull up the plane (you will see the same way on supersonic fighters).

Not that there is no shock wave even before the sound barrier in the transonic regime. It just moves from the wing profile in front of the profile.

You typically get something like this graph, no sudden change.

Pitch trims may not be functional if there is sufficient load against them. See other answers for examples where leaning into the dive was necessary to unload the trims.

Could an airliner exceed Mach 1 in a zero-G power dive and safely recover?

There is only one answer here and that is NO, especially for the A320 in your example (there are other airliners better suited to tolerate higher transonic speeds).
Yes, it's possible to recover from such a condition, but nothing about it would be safe.  Recovering from this condition would be a situation in which you would consider yourself lucky, because the aircraft is simply not designed to operate under such conditions and catastrophic mechanical failure becomes a serious possibility.  Successful escape will always be on account of some degree of good fortune (ie: things you didn't plan, didn't think to plan, or couldn't plan, but that went OK and conspired to save your bacon).  The aircraft will likely suffer damage - with luck, it isn't critical damage.
Who is to say what the weak link would be, but it could be anything - a single mechanical component could mean the difference between life and death.  Does your plane have a critical support that's on the weak side of the bell curve?  Maybe a sister craft made the next day might survive a dive that yours would not.  Each plane will fail in a different way depending on whatever component happens to fail first.  When you're outside the envelope there are no guarantees - you might get lucky, you might not.

How do I get out of this in one piece?

What's important to understand is that the outcome in these situations becomes highly unpredictable.  Subtle changes in the test conditions, weather, environment, etc, can all cascade quickly into an uncontrollable situation, regardless of the pilot's skill. Despite your best efforts, the result may still be fatal.
That someone managed to do it successfully once is not an indicator that it would be safe to attempt again.

how much faster can I go before I need to start this process of getting out in one piece?

It's already too late.  The faster you go, the higher the chance you won't make it.

Supersonic aircraft are specifically designed to minimize the destructiveness of the pressure waves they generate and otherwise stiffen the airframe against the residual stresses that result.
Airliners, by contrast, optimize entirely for sub/transonic cruise speed and, critically, efficiency.  They incorporate no such design features and in fact have efficiency-minded elements of their design that make them particularly ill-suited for supersonic flight. As such, they tend to generate more disruptive and destructive pressure waves than supersonic aircraft during transonic flight.
Because supersonic stresses appear in largely different areas of the aircraft than subsonic stresses, airliners are also far less structurally capable of withstanding them.  Doubly so these days because the aircraft all have a variety of overspeed protection systems which allow the designers to certify the aircraft closer to the danger zone of the flight envelope.
From : IATA -- Loss of Control In-flight (LOC-I) Prevention : Beyond the Control of Pilots

4.8.4     Benefit of Overspeed Protection Systems
Automated overspeed protection systems may be seen as something designed to help avoid a dangerous high speed condition. At least that is the perception of many pilots – why else would a designer make the effort to develop and certify the system if not for the benefit of protecting the aircraft? Well, there is one big commercial aspect which is not so well known, and that is significant aircraft weight savings. By installing an overspeed protection system the designer is permitted by the standards to bring VMO/MMO much closer to the design dive speed[emphasis mine] and hence the speed at which the airframe will eventually start to flutter and disintegrate. In other words, the structural integrity margins between the maximum normal operating speeds used by the pilot and the speed at which damage will occur may be narrower, meaning that the aircraft structure need not be as robust. Structural strength usually equates to weight in aircraft construction so ultimately the overspeed protection system allows a lighter overall aircraft structure.

Airline travel is such big business that the rules bend to allow them to shave efficiency right up to the margin.
For a relatively recent real example of it not ending well : Adam Air 574 : 737-400

The aircraft reached 490 knots (910 km/h) at the end of the recording, in excess of the aircraft's maximum operating speed (400 knots (740 km/h; 460 mph)). The descent rate varied during the fatal dive, with a maximum recorded value of 53,760 feet per minute, roughly (531 knots (983 km/h; 611 mph)). The tailplane suffered a structural failure twenty seconds prior to the end of the recording,[11]:52 at which time the investigators concluded the aircraft was in a "critically unrecoverable state". Both flight recorders ceased to function when the 737 broke up in mid-air at 9,000 feet above sea level.

The cause was determined to be pilot error.

A Question about whether something is possible is not a question about safety.

@2NinerRomeo It is when the question explicitly asks about safely recovering. The answer to that will largely depend on the aerodynamic characteristics of the jet in question in the transonic regime. Also, while the DC-8, 747, etc. are designed to fly relatively high in the transonic regime without actually going supersonic, the A320 is not. MMO (Maximum operating Mach number) is only 0.82 for the A320. By comparison, that was a normal cruising speed for the DC-8. The test pilot quoted in Dave's answer mentioned later in the article that MMO was 0.95 for the DC-8.

@2NinerRomeo I agree, but this question was specifically whether you could do it safely.  The very first quote was the exact title of the question at the time that I answered.  OP has since edited it to somewhat alter the meaning.

@reirab Indeed.  And with overspeed protection systems they're allowed to push MMO pretty close to Vd.  I've updated with some discussion from IATA.

I think you have mis-interpreted the question - to me, saying "safely recovered" means "alive/in one piece", nothing more.

@MikeBrockington Yes, and there is a huge risk of that not happening.  There is a terrible predisposition in cases like this to credit the pilot for fancy flying that saves the day - and a risk of taking a situation like this to feel equipped to deal with it in the future.  Everyone likes to feel like a hero.  I'm saying that's a fallacy, and a dangerous one, because the result the next time may not be so favourable, even if one does all of the things other answers here have suggested (or what worked in other cases).  It's a form of frame challenge and it's very deliberate.

My point is that you lead off by saying: "There is only one answer here and that is NO" but actually the shortest possible answer is "YES". Massive caveats are necessary, but still...

@MikeBrockington You're effectively trying to start a debate over the definition of the word "safe".  I think that's not terribly productive.  Others answers discuss techniques, etc.  I felt this answer rounds out the discussion with a rather practical view of why those techniques fall under the umbrella of last-ditch-efforts to recover from a very serious situation that doesn't necessarily have any guarantees of surviving. Whether deliberate or accidental, going supersonic in a short-haul airliner is an emergency that may not have a happy ending, regardless of the pilots actions.

No, I'm not. I'm saying that you should entirely ignore the word "Safely" in the title - the body of the question does not support the existance of the word. The core of the question is "is it possible to recover", to which the answer is "YES, but unlikely". Most people like to know why their answers are downvoted. If you don't, I'm happy to delete.

@MikeBrockington As I noted above, OP edited their question after I had posted this answer to alter its meaning. This is generally "bad behaviour" on the stack (also linked above) because it invalidates the work of people who answered the original question and not the chameleon question it turned into.  Why do you insist on making me repeat myself?  If you have another answer to add, by all means go ahead.

This recent video about the X-15 went into excellent detail about the challenges associated with achieving high mach numbers. Some of the lessons are instructive about the challenges in moving from subsonic to supersonic flight. https://youtu.be/7zR26e504uI

It really depends on the aircraft. A DC-8 is known to have done this. (https://www.airspacemag.com/history-of-flight/i-was-there-when-the-dc-8-went-supersonic-27846699/) There are 2 sources of stress on the airframe in this situation- airliners aren't designed to fly past Mach 1 (except the Concorde and Tu-144...), so there's one issue. There's also the issue of the recovery, as airliners have G-limits.

"In pitch, when an input is made on the sidestick, the flight control computers interpret this input as a “g” demand/pitch rate. Consequently, elevator deflection is not directly related to sidestick input. The aircraft responds to a sidestick order with a pitch rate at low speed and a flight path rate or “g” at high speed. When no input is made on the sidestick, the computers maintain a 1g flight path." http://www.aviationchief.com/airbus-control-laws.html

So, an Airbus airplane will prevent you from introducing a too-high g-load. In the clean configuration, an A320's g envelope is -1 to +2.5 g, and the same is true on the Boeing 737. (https://www.theairlinepilots.com/forumarchive/a320/a320-limitations.pdf) (http://www.b737.org.uk/limitations.htm#Flight_Manoeuvring_Load_Acceleration_Limits) I can't find anything indicating the presence of a G-limiter on Boeing airplanes, so you'd have more careful.
How long you could go before initiating recovery depends on where you are. If you're over the Alps or another mountain range, it would be wise to initiate recovery as soon as possible, since you'll be limited by g-load on the rate you can recover. The maximum speed you could attain would depend on the airframe; MMO for the 737 is 0.82 Mach, so you're already having issues. Per the A320 TCDS the MMO of that airplane is also 0.82 Mach.
Given this, it's possible that you might survive, but you're risking damage to the aircraft and recovery isn't guaranteed. During the recovery, you may need to actually pitch further into the dive to unload the trims, so that's increasing the risk that A) you push the airframe a little too far, and B) you hit the ground before you recover. Nothing about it would be safe. The A320 and 737 would be bad choices, other airliners have higher MMO's. The Concorde might be able to do it but it has the same 2.5g limit. Ultimately, the margin for error is extremely low and it's not possible to do this safely.

It Theoretically could, but not likely due to the fact that when you are pulling up at the speed of sound, you would be exerting more g forces that the plane could handle. Also take into account, Pilot Error, Density altitude, weather factors, Weight and balance and the recent inspection of the aircraft. These factors would greatly decrease your chances of survival. Here is a link that shows for example what a typical structural chart would look like. ( One for Each aircraft model)Structural Chart for GA Aircraft

Past Vmo/Mmo (well, probably Vmd) there's no telling if you're gonna be able to recover. AFAIK it's not about the G-forces, it's about the aerodynamics of the wings and control surfaces. The elevator just might not work anymore to effect a pullup, and the ailerons may become useless. You're likely to be left with an uncontrollable aircraft whose parts will tear off at some point as the speed keeps increasing.
The Learjet 55 had a stick puller (preceded by a nasty aural warning) that was intended to prevent it going too fast. There was a reason they put that in, and I'm sure it had to do with someone's soiled underwear!
Nevertheless Bill Magruder's idea to push rather than pull on August 21, 1961 in his DC-8 was bloody brilliant and worth remembering.
Just don't go there!

Mach 1 is approximately 67,000 feet per second.  At a max ceiling of maybe 40,000 feet, an airliner couldn't even get close to Mach 1 speed in that distance.  Given enough height it could do it but it would be starting the dive from Space or very close to it.

While speed of sound in air depends on temperature, it is for sure never 67,000 feet per second (that would require a temperature of 1,037,138 °C, where air is no longer an ideal gas and the formula doesn't hold any more). Speed of sound at sea level is about 1125 ft/s. It is somewhat lower at higher altitudes (due to lower temperatures).

67,000 feet per minute.  ftfy  ;)   67,000 feet per second is over 20km/sec.  That's almost double escape velocity.

Yeah, better check your math and conclusions.  DV for inaccuracy.

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authors: Vladimir F Героям слава


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Can countries introduce new aviation policies unilaterally?
Let's say some country intends to introduce a new aviation policy that conflicts with ICAO regulations, like only aircraft certified and approved by our government can fly in our airspace. Can they do that unilaterally? Has it ever happened?
For instance, Russia may declare a country as enemy country and it may use its equipment (e.g reconnaissance aircraft) to spy on this enemy country. In this case enemy country may start defining its own policies and make sure that defense or civil aviation equipment/software are used in compliance with these new policies.

A sovereign country can introduce any laws it wants to, even if they're wildly impractical and/or annoy all their neighbours. I'm not sure what sort of answer you expect here.

Aircrafts need to be certified to operate under FAA/European/Russian... regulations in terms of safety, noise, etc.
For instance, in Europe EASA is the authority "for the airworthiness and environmental certification of all aeronautical products[..]".
Sometimes countries actually want to introduce new policies.
One of the most famous was in 1971, when "The US, India, and Malaysia all ruled out Concorde supersonic flights over the noise concern[..]" as reported here on Wikipedia.
Another one about aircraft noise was in 1999, when "The EU's proposed noise ordinances effectively prevented the use of hush-kit outfitted aircraft in Europe[..]".
So every country already has its own regulation.

"EU" isn't a country. EU members are the therefore the exception to the rule; they're the only countries who legally can't have their own regulation.

@MSalters: I'm not sure this is correct, EU member states have their own regulations (not specific to air regulations). Only a set of EU regulations are in effect in agreed domains. In addition EU directives must be implemented locally to have effect. A patent case is the about the labor regulation, which varies a lot between member states.

@mins: It would take more than 600 pages to explain EU rulemaking, so this is necessarily a summary, but the process differs from area to area. AIr traffic being by nature more international is an area in which the EU has more authority. Practically speaking, EASA rules do not require local adoption.

@mins: That's part of why rulemaking in the EU is so complex; it goes in both directions. In some areas national governments delegate to the EU, in other areas the EU delegates to national states. Here the administration of small airports is delegated from the EU (who has authority) to France (who is more capable of handling details).

@MSalters Again, not correct: EU delegates nothing to member states, this is the other way. for transportation, which isn't an exclusive competence, EU can only rule if members are unable to achieve some action (see TEU title 1, art 5-3). EASA (actually the European Parliament) as indeed exclusive competences but only in some domains (e.g. safety), the rest (e.g. air operations) is a shared competence between the state and EASA, see this.

Technically, yes.
There are a number of national regulations barring specific aircraft, for example there are several African airlines that may not operate in Europe.
However, in general there is mutual agreement that other countries' certification agencies are equally capable of assuring the airworthiness of planes, so there is no safety issue here, and the remaining question for a bureaucracy is whether to burden oneself with extra paperwork.

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text:
Really love aviation but have a computer science degree. What kind of jobs could I possibly get which involve aviation?
I really want to work in the aviation industry. Is there any way I can put my computer science degree to use in this industry.

Avionics? Can you provide more detail on your aspirations?

Don't forget ATC hardware and software.

Possible duplicate of http://aviation.stackexchange.com/questions/1839/which-companies-develop-software-for-airplane-systems?rq=1

Computer science covers a lot of different things. What are we talking about here? Algorithmics? Networks? HCI? Database management? Cybersecurity?

Me too! But 15 years in the software industry and I'd love to work in Aviation.

I'm voting to close this question as off-topic because careers advice is too specific to the individual asking for that advice to be of general interest.

This would really be a better topic for chat than the site...

If you want to work on something that's actually on-board the airplane, I'd recommend getting as much embedded development experience as you can.

reirab is right. For that you want 2 languages, Assembly and C. Every processor has it's own version of assembly these days, but they are mostly very similar. I'm told most of them run compiled C too. Assembly is the starting point but a lot of CS folks these days have trouble with it because it's so low-level, just one step above machine code. I don't know your situation so I'll just leave it at that.

I'm not sure if this question comes within the scope of this site the way it is phrased.
Anyway, Aviation industry is highly interdisciplinary and has a lot of scope for computer science engineers like,

Design of aircraft subsystems
Development of programs for design and analysis of aircraft components (CAD, CFD etc).
Instrumentation and testing of aircraft systems
Development of aircraft control systems (e.g fly by wire)
Aircraft testing and telemetry.
Aircraft maintenance, which is becoming software intensive.
Software for Airborne (avionics) and Ground based systems (e.g. Air traffic Management).
Development of aircraft display systems.
Software for communication systems for UAVs.

This list is by no means exhaustive. In most parts of aviation, there is a requirement for computer science engineers.

Not to mention the admin side of things, even if you're not directly working on the software that makes the aircraft fly. Revenue Integrity, route planning etc - airlines churn through a huge amount of data. I was amazed when I worked in Airline Revenue Integrity just how much data they crunch daily, even at smaller airlines.


text:
Are air marshals on every flight?
These guys say (in the discussion) that they were the only three passengers on board.
Does that mean that there was no Air Marshal on board (or one of them was?).
Aren't air marshals present on every flight?

This sounds like the setup to the poker adage "Look around the table, if you can't identify the sucker, you are the sucker". It looks like the photo shows the 3 men in Economy class, since they flight attendants didn't let them go up to First Class for free, it's likely that there were already passengers in first class, perhaps the air marshalls were among them.

Specify 'every flight'. Every commercial flight? Every American commercial flight? Every international flight? What exactly are you asking?

The exact number of air marshals is not public information, and they certainly don't disclose what flights they fly on or other operational details. However, the number has been reported to be on the order of ~3,000-4,000 and reports indicate the number has decreased somewhat since then. All of them are, of course, not on duty 24/7/365. There are around 87,000 flights a day in the US alone, but only around 28,000 are commercial passenger flights, where air marshals are presumably most likely (hopefully there's not a need for air marshals on military flights, for instance).
So for some back of the envelope math, let's conservatively say there are 3,500 air marshals who all work five days a week, they all work alone (in reality, they appear to work at least in pairs), and they somehow manage to average protecting four flights a day. Even with these conservative assumptions, that would only be 5000 flights/day covered by air marshals. From this, it should be clear that there cannot possibly be an air marshal on every commercial flight in the US.
The President of the Air Marshal Association/CWA (their union), not entirely a disinterested party, agrees:

"There are around 30,000 commercial flights per day over the U.S.," says Casaretti. "If you were to attempt to place a team of just two FAMs on each flight, it would require an agency of over 75,000 FAMs (accounting for training and days off). FAMs cover a very small percentage of commercial flights."
Which flight air marshals get on is determined by a computer program that assesses the probability of threat based on the aircraft, departure and destination cities, as well as the amount of fuel on board. This is the threat matrix that comes out of the missions operation center.
The TSA will not release statistics on the number of air marshals. TSA's Pascarella acknowledges only "many thousands." But Biles estimates that there are approximately 3,300 FAMs and of those, 34% are filling ground assignments in training, operations and management.
"We call them 'chair marshals,' riding out their career in management," says Biles. That leaves 66% of the workforce to perform in-flight security duties.
"If one accounts for vacations, sick leave, medical leave and days off, some air marshals working in operations have told me that this accounts for less than one half percent of all U.S.-flagged aircraft being covered by federal air marshals," he says.

"less than one half percent of all U.S.-flagged aircraft" This is, of course, a meaningless statistic, since many US-flagged aircraft aren't on commercial flights.

David, how is that meaningless? You seem to know exactly what that statistic meant... Enough to complain about it.

@ermershel It's meaningless because air marshals aren't supposed to be covering non-commercial flights. It's a true statistic, but one that is ultimately irrelevant (though it's designed to sound relevant in order to exaggerate the actual situation.) This would be like saying TSA only scans passengers at 10% of U.S. airports while failing to mention that that 10% happens to be all of the airports with scheduled passenger service (I just made that number up for example... I'm not sure what the actual percentage is.)

Ah.. An irrelevant, not meaningless statistic, then.

Also, how do you know what the statistic is designed to sound like. It didn't fool any of us into thinking it was relevant.

That's why I said the head of the Air Marshal Association/CWA is not exactly a disinterested party here. The statistic implies that air marshals cover a dangerously low number of flights, but the universe of flights being considered includes everything from passenger jets a few miles from the White House into DCA to a crop duster in an Iowa field.
Of course, there's also the random deterrence theory. You don't know whether an air marshal is on board a given flight, so, as the theory goes, it's not worth risking that one is present. The same applies to transit fare inspections, for instance.

@ermershel irrelevant means that it adds no meaning to the current context, and thus is meaningless to the discussion. There's a difference between general nonsense and something that adds no useful information. In this context, irrelevant and meaningless are synonyms. Likewise, we know what the statistic is designed to sound like because of context - a union boss speaking publicly only makes statements designed to forward the goal of growing their union. We have enough history on that one. It's a very short jump to understand what's being said here and why.

Air marshalls are not on every flight. I was recently at a computer science seminar by Milind Tambe, whose research team developed the software that the Federal Air Marshal Service uses to randomly choose which flights get marshals. (It's also used for security patrols at LAX, coastguard patrols at various ports and even for anti-poaching patrols in Uganda's national parks.) Note that "randomly" doesn't mean uniformly at random: certain flights are more likely to be covered than others, depending on the perceived level of threat.  But the fact that they choose which flights get marshals clearly means that some flights don't.
For those who are interested, Prof. Tambe's website has a lot of information, including some explanatory videos.

Air marshals are certainly not on every flight. With 80,000 flights daily in North America it would be nearly impossible, and most flights are low-risk. Billings, MT to Denver, CO in a Dash-8 simply isn't worth the effort to either police it or hijack it.
Higher ratios of marshals to flights will be found going into the major centers, and it likely approaches 1:1 going into the DC area.

Billings, MT to Denver, CO in a Dash-8 simply isn't worth the effort to either police it or hijack it.  That depends on your objective.  If a bad guy really wanted to incite random terror, picking on a soft target that's supposed to be so boring as to be beneath notice would be a really effective way to accomplish it.  Just saying.

Don't tell C.O.B.R.A.

That's a fair point @MasonWheeler. Of course, said bad guy could pick any number of targets with less security than aviation too.
The real change though is in the attitude toward hijacking. Post-9/11, passengers and crews are prepared to do whatever they possibly can to defend themselves against an attack on board. There's no longer much reason to believe that everybody can cooperate and get away unharmed. While that change doesn't eliminate all threats to aviation, it would make it much harder for anybody to pull of a 9/11-style attack today.

@Zach: Agreed. The 9/11 attack was a hack, a trick that could work exactly once.  But that doesn't mean they couldn't try something else.


text:
What is an executive pilot?
I've been reading the transcripts from the July 17 and 18 1962 "Qualifications for Astronauts" hearings before the special subcommittee on the selection of astronauts that was organized to know if women could become astronauts. In the record (see page 10), the qualifications of each of the Mercury 13 are listed. Rea Allison and Irene Leverton are each stated to be an "executive pilot". What is an executive pilot?

Absent context, if I were to take a guess, I'd suspect it's about what we'd call today a "corporate pilot" - i.e. flying corporate executives (and others) around in whatever it is they own, be that a King Air, a Learjet, a BBJ, or whatever. It's potentially jet time, but not remotely as demanding flying as military fighters.

Yes, this article does mention Rhea Allison (Rhea Woltman) as "secretary and executive pilot for a small aircraft sales and engineering firm", so it's a valid question. Please refrain to close it without trying to help.

Thanks for adding the link to the transcript - close vote retracted.

@mins - Pointing out the need to see the term in context, i.e. a link to the document that generated the question, isn't being helpful? The initial version of the question lacked details, I pointed that out, and the question has been improved. How is that being other than helpful???

@RalphJ: What is the point to ask for closing the question after an hour? When there is one close request there are soon more from followers. Closing could wait a few hours or a full day. That said, I was not aware you were the one to ask for closing and at the same time suggesting the improvement which I agree is fair.

@mins if closing needs to happen, sooner is better than later. if the fix comes after the closing, there is the re-open queue.

Few texts mention Rhea Allison (Rhea Woltman) as "secretary and executive pilot for a small aircraft sales and engineering firm" (additional copy). Other mention her as a regular commercial "pilot": When she started the astronaut curriculum for Mercury, "Woltman was working as a charter pilot in Houston".
There is nothing particular with executive pilot in the sense of a pilot with particular a rating or function. Online search on this sentence returns nothing except describing a position of a pilot for executives. This is confirmed by Termium Plus, the Canadian Administration translation resource between English and French:

Executive pilot: Pilote chargé du transport du personnel de direction.

which means in English: Pilot in charge of carrying executives, similarly, an executive jet means a corporate jet:

Many businesses use executive jet charters when time and money are at
a premium. Private executive jets are available for flights from your
local airport to the nearest airport to your destination and are
flexible to fit around your business travel plans.

Executive pilot is then synonymous of corporate pilot.

all_licenses: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/


text:
Who decided that the Boeing 737 MAX planes that were airborne when the grounding was issued cannot enter and land in EU air space?
On March 12th, 2019, EASA grounded the Boeing 737 MAX series by publishing their Emergency Airworthiness Directive 2019-0051-E (AD):

Effective Date: 12 March 2019, 19:00 UTC
 [...]
Required Action(s) and Compliance Time(s):
From the effective date and time of this AD, do not operate the
  aeroplane, except that a single non-commercial ferry flight (up to
  three flight cycles) may be accomplished to return the aeroplane to a
  location where the expected corrective action(s) can be accomplished.

The PDF document was created at 17:12 UTC and went into effect practically immediately. The AD does not specify any particular instruction for actions concerning flights already airborne.
Of course there were a number of long-haul flights en-route, that clearly started before the publication, and were scheduled for landing in the EU hours after the effective date/time of the AD. Closely related questions have already been asked on Avitation SE:

What happens to an airborne plane when its type is grounded by an authority?
Why would a flight no longer considered airworthy be redirected like this?  (Smart Wings QS 1201 was scheduled for DXB 15:30 UTC - PRG 23:20 UTC)

After March 12th, many people were convinced that EASA has forbidden entry or landing for the 737 MAX in EU air space. I cannot read that from the directive or any other reliable source.
We all agree that operation of a plane shall not be finished mid-air. The AD could not be followed literally for flights like QS 1201. Unless this case is covered by a different applicable document, EASA failed to give a clear directive.
Emergency ADs shall always serve the purpose of aviation safety. I cannot see how diverting numerous flights on very short notice can be safer than allowing landing at the planned destinations.
For comparison, this is how the FAA worded their AD on March 13th in this corresponding part:

This Order is effective immediately. This Order prohibits the
  operation of Boeing 737 MAX airplanes by U.S. certificated operators.
  This Order also prohibits the operation of Boeing 737 MAX series
  airplanes in the territory of the United States. Boeing 737 MAX series
  airplanes covered by this Order, if in flight at the time this Order
  is issued, may proceed to and complete their soonest planned landing,
  but may not again takeoff.
Special flight permits may be issued [...] including to allow non-passenger carrying flights, as needed, for purposes of flight to a base for storage, production flight testing, repairs, alterations or maintenance.

FAA's AD covers the case of airborne 737 MAX explicitly. On the contrary, the EASA AD requires interpretation at this point, and therefore this is my question:
Who had the right and duty to interpret this AD and to decide what should happen with the B737 MAX in flight?

Was it ATC in the role of an executive authority?
Was it the Airline that is risking its certification or wanting to minimize storage fees?
Was it the PIC who is risking a hefty fine?
Or am I missing something entirely?

As far as I know (and in AD interpretation, I admit what I know is rather limited), information like this normally only applies before dispatch, as nobody can expect the ADs to be telexed into the flight deck and thus they cannot influence flights already departed.

This is just simple common sense. The failure modes encountered were all on takeoff. It would have been really stupid to prevent aircraft in flight after the AD was published from landing in EU airports or entering EU airspace. Besides, if they did that the pilot in command always has the right to override the ban and inform air traffic controllers that he/she will land, period.

@JuanJimenez Common sense does not apply to legal questions.  ;)

@bogl that's a hilarious comment. :)

With regard to the failure modes previously encountered all being on take-off, if I recall correctly, the previous failure on the Lion Air aircraft was early in the cruise rather than take-off.  But my recollection may be incorrect.

@PaulSaccani Yes, the fatal descend started in early cruising. But there was also some hiccup during the climb, and they asked ATC to confirm their alitude 1.5' after take-off.

The previous failure on the Lion Air aircraft did not result in an accident.  It was resolved by using the trim switch to correct for MCAS activation, cutting out auto trim and completing the flight using the trim wheel.  The later crash occurred during the climb phase of the next flight.  It is likely that there may have been other failures that were treated as trim runaway - the maintenance action which be the same and MCAS involvement would likely not be recognised.  However no likely cases are present in the FAA SDR database as best I can determine.

The operator's airworthiness department interprets the AD and informs the operations department and senior management.  Ops decide how to deal with airborne aircraft.
The EASA AD actually had more generous continued flight provisions than the FAA issued AD.  It was in no way intended to prevent aircraft in flight from landing.  Airworthiness would immediately talk to operations.  Operations would decide what to do, though in most cases a few phone calls would be made to senior management.  If the aircraft can't make it back to a 'home' port, that pretty much dictates what is going to happen next (continue to destination).  In the subject case, a number of aircraft were airborne and capable of returning to a home port.  So you need to figure out what to do next - continue flying to your EU destination and get your passengers there with minimum inconvenience (with possible adverse publicity for not discontinuing the flight as soon as possible), or simply get the aircraft back to base so that you don't have it stuck somewhere needing maintenance (and reading between the lines, Ops and Airworthiness would be concerned that the recovery might become more complicated than the 3 flight cycle limit ferry suggests).  So better to get your pax down ASAP, at a port where you can easily carry out whatever rectification is needed, and importantly too, also one where you have more aircraft available to get your passengers to their destination without having to do positioning flights.
In some cases, such as TUI, they elected to divert the aircraft to the nearest suitable port, regardless of destination or home port convenience.

Would you mind to indicate how you know that? Is it first hand knowledge, do you have a source, or educated guess?

Not at all, thanks for asking.  How the system works to deal with these kinds of problem is first hand knowledge.  TUI diversions to nearest suitable port was an observation from watching what the global 737 Max fleet in the air at the time was doing.  Given the short compliance time, there must have been some heated discussions between the various sections of affected airlines - given their competing priorities.


text:
Why does V1 increase with headwind and decrease with tailwind?
Can someone explain why V1 increases with headwind and decreases with tailwind? I read such a phrase in my ATPL(A) performance textbook, but without further explanation.

V1 is the maximum airspeed you can accelerate to and then stop again without running out of runway. For the sake of simplicity, let’s assume that happens at the midpoint of the runway.
If there is a headwind, i.e. your airspeed before starting the takeoff roll is positive, then you will achieve a higher airspeed at the midpoint.
Likewise, if there is a tailwind, i.e. your airspeed before starting the takeoff roll is negative, then you will achieve a lower airspeed at the midpoint.

What you describe as V1 is actually only an upper limit on V1. The actual value for V1 could be lower and it could be limited by other speeds, like e.g. VR (which does not depend on wind) or Vmbe (which depends on wind speed since kinetic energy w.r.t. the ground is relevant for braking).

You can even see that effect in a realistic simulator like X-Plane when using a glider that has a rather sensitive (regarding low air speeds) speed indicator. Or, even in more simple words: That's how kites work ;-)

Some additions to StephenS answer, here is a more detailed picture:

VR is the speed at which you should take off your aircraft, as defined by the aircraft weight, altitude, temperature. This is provided by aircraft performance tables.
V1 is the maximum speed at which you may still abort take-off while expecting a stopping before end of pavement. This depends on your aircraft ability to accelerate (thus depends on its performance: power, weight, altitude) and then to decelerate (depending on aircraft weight, brakes capacity, and (mostly!) remaining runway length).

Said otherwise, V1 is basically based on the runway length and aircraft performance-of-the-day. The closer V1 is from VR the better, as it means less time between V1 and VR for bad things to happen (e.g. engine failure).
And then, considering the wind:

Some headwind means your aircraft needs less time and runway distance to reach VR, leaving more runway length to decelerate in case of rejected take-off; V1 is then higher (which is good).
On the contrary, with some tailwind your aircraft will take more runway length to reach VR, leaving less distance (and time) for deceleration in case of rejected take-off; V1 is then lower (which is not so good).

indeed! updated

A headwind will also decrease braking distance somewhat, while a tailwind will increase it.

lol thanks @jamesqf i was literally about to ask that! heh

@Fattie: Don't know how much it would affect a commercial airliner, but it's very noticable in a small plane.

Aside from the fact that with headwind you're starting (from zero groundspeed) at an above-zero airspeed, does headwind really reduce the time to reach VR? Airspeed acceleration should be the same, shouldn't it?

@Codebling At first order of magnitude, yes, headwind does not really change the aircraft acceleration (*). But the take-off distance will significantly vary, as the time/distance to reach VR is the integration of acceleration from initial airspeed; therefore if airspeed is already positive at take-off start thanks to headwind, the aircraft will need less time and distance to reach VR. Note (*): aircraft acceleration is very likely not constant with airspeed, depending on engine type, propeller setting, etc.

Don't count on it, though, on turbine airplanes big enough to use "Flex" takeoffs.   This is when an aircraft has "more runway than it needs" for a full-thrust takeoff at its weight, temperature, wind, etc.  Therefore, they reduce thrust somewhat, trading a longer runway roll for much reduced turbine engine wear and tear.
A lot of math goes into this, since Flex is actually implemented by lying to engine computers about ambient air temperature, making it over-estimate engine pressure and temperature values, and rollback somewhat to protect the engine.
V1 is all about your last chance to abort a takeoff and still be able to stop before the end of the runway.  The point along the runway  varies by all the above plus your momentary ground speed.
If I were king, there'd be a rail on runway edge with a trolley, moving toward you, marking your "last abort point" at your data and ground speed.  But instead, they use above data (plus assumptions about your acceleration) to capture that "last chance" point not even as a ground speed, but as an airspeed.  That is V1.
Getting from "Harper's trolley" to an air speed computed prior to start of takeoff roll is also a whole lot of math.
A takeoff roll starts at a ground speed, but ends at an air speed.  As such, a plane with a nice headwind has less actual accelerating to do.
Conversely a rejected takeoff starts at an air speed, but ends at a ground speed (of 0). Thus, a good headwind means less actual decelerating to do, which can happen in less runway distance.  So right off the bat, V1 can happen later down the runway with a head wind.
However, other answers are only correct (V1 being higher) if you always say "who cares about turbine maintenance".   As soon as Flex enters the picture, all bets are off.  A runway you can use effectively in a strong tailwind will certainly warrant Flex in a strong headwind.  You have two complex calculations - V1 and Flex - both using a lot of parameters.  V1 may remain the same or even lower a bit.

Simple. V1 is the airspeed that you can accelerate to and still stop on the remaining runway. Except for minor effects wind has on aircraft acceleration, a headwind or tailwind is not relevant to the groundspeed/runway remaining when this is no longer possible (this is determined more by braking/reverse thrust).
So this will occur at pretty much the same point on the runway, and at the same groundspeed regardless of the wind. Therefore, with a headwind, you will have a higher airspeed when you get to this same point on the runway.
Except for the fact that we have always done it this  way, and as in all things, accepted practices resist change, it might be argued that with ground speed indicators as ubiquitous as they are today, ground speed might be a better determinant for V1 than airspeed. I would be curious to see what a more detailed analysis might indicate about that.


text:
Can we replace an attitude indicator with a ball half full of liquid?
Attitude indicators (artificial horizons) use a gyro to display pitch and bank.
I was wondering if it would work to use a ball half full of liquid to replace the artificial horizon (using the water level as reference)?

Nope.  In a perfectly flown turn, the ball of liquid would appear to indicate level flight.
You might argue that it could replace the "ball" of a turn & bank indicator, but that's about it.
It would also be tough to read in turbulence.
See also this YouTube video showing Bob Hoover pouring iced tea while flying the plane through a roll, even while inverted.  Your liquid would behave similarly.

The bob hoover video is a great demonstration of the problem!

One could perform a well-executed loop with the water in the ball hardly moving at all

The video behind this link was removed for copyright reasons.

This is similar to the "use a plumb bob / fuzzy dice" idea.
Happens all the time where VFR pilots fly into IMC, and rely on their sense of balance (from their inner ear) to keep the plain straight and level.  The forces acting on the inner ear are the same as acting on the plumb bob at left.   How are we doing?

Look at the plumb bob on the left.  Looks great right, hanging straight down.  Even the toy gyroscope on the right seems to agree, in the larger sense of motion anyway.  Don't know why it's tilting like that.
By the way, somehow the right-side PFD got set to the Russian style, but they average out to level, right?
OK, here's what's really happening.

  Now we see.  The airplane is banking, but it's doing so in a coordinated turn, so the sum of gravity and centripetal force balance out and provide straight vertical acceleration.  This could be the classic bank/spin that happens when VFR pilots fly into IMC and try to use their inner ear to fly what feels like straight and level.   The ear is fooled, as is the plumb bob.

 The gyroscope is not fooled, because it is resisting the change in orientation that happened when the aircraft banked.


text:
Why does a Fenestron tail rotor require so much speed compared to an open rotor?
As explained in this video(@3:22) by PilotYellow, a Fenestron tail rotor spins 10x faster than the main rotor while a traditional tail rotor only spins 6x faster.
Why there is so much difference? Aren't ducts supposed to create more thrust? Also, aren't more blades supposed to created more thrust?
What's the reason for the difference?

The speed of a rotating wing, no matter if it is used in a propeller or in a rotor, is normally limited by the onset of transonic speed on its tip, speed which is linearly proportional to its radius/diameter.
I think the H145 is a good example to answer your question: When it was still named BK117, it had a conventional tail rotor with a diameter of 1.9m. The newest version has a fenestron instead, with a diameter of 1.1m. Their ratio is 0.6 which is exactly the number given in your video.

BK117 with conventional tail rotor (source)

BK117-D3 aka H145 with fenestron (source)

Propellers and rotors create thrust by accelerating the air that passes through them. A smaller rotor blows a small amount of air at high speed, a large one blows a large amount of air at low speed, but the force (or momentum change) is the same. So when you make a tail rotor smaller, you have to spin it faster to get the same thrust.
Ducts can improve efficiency, but they're often over rated. They reduce tip loses, but tip loses are small on long, thin blades because the tip is a small part of the overall blade. As the blade gets shorter and more highly loaded, tip loses increase and it becomes worth adding a duct.
Tip loses mean that an area near the tip of a blade isn't making much lift. So you can think of a duct as extending a blade's span by (very roughly) one chord-width. It's not nearly enough to make up for the blade being only 60% of the original length.

I think you are looking at this backwards. The goal going in is to lower the weight of any given tail rotor assembly and it's drive system, both for direct weight savings and because the moving parts are relatively expense on a per-pound basis. The easiest way to do that is to make the rotor smaller. Spinning it faster saves weight on the drive components at equal power delivery. So the goal is to design a rotor that is as small and fast as possible that still makes the target thrust at the target power. As stated in Robin's answer, ducts can considerably increase the effective diameter of a prop (when viewed at equal efficiency). Ducted props move nearly same amount of air as a larger unducted prop, but with very different span loading, a higher advance, and, because they can push the rpms up, run lower torque through the drive.

The fenestron is quite a bit heavier and less efficient than a conventional tail rotor and was added to the ex-MBB, now Eurocopter helicopters after the French side insisted on it.

Everything about the description of the handling issues suggests it is more efficient during normal operations. It has less to give during extreme control demands - that's a typical side effect of improvements to static efficiency. It's why modern small trucks need so many gears when the old ones had three of four - the new engines are more efficient and lighter, but don't have any reserves or torque droop to provide adequate drivability over wide gear ranges. Now we can either say they suck, or we can match them to an appropriate transmission.

@PeterKämpf Okay, I think I understand your point wrt my post's second sentence. I'm going to tweak the wording a bit there.


text:
Will computational fluid dynamics (CFD) ever be 100% correct?
CFD results never match real world numbers especially in turbulent 3D complex flow...
What stops CFD being perfect, and will it ever be 100% correct? If the Navier-Stokes Millennium problem is solved, will CFD then become perfect, or is turbulent flow simply so complex that no math can describe it properly?

Re "never match real world numbers": What is the deviation (in %)? What deviation can be tolerated?

Can reality ever be 100% correct? The universe has a granularity, too.

@PcMan So the exponential problem is actually solvable in linear time because computer power grows exponentially, too. 200 years, give or take a few. We should focus on solving aging first, apparently. How is Kurzweil doing, btw.? Still chugging 100 pills a day?

There exists yet no complete model of physics, so no model of anything is ever 100% correct, analytical or numerical.

@Peter - Reinstate Monica: But there are fundamental limits to the growth of computing power.  E.g. it's hard to make circuit traces less than one atom wide, or boost CPU frequency into the THz range...

From a computability perspective: there are Newtonian physics problems that are undecidable due to Halting-problem issues. I do not know if any such encoding exists for CFD. (Essentially: there are systems that diverge to infinity in finite time. Encode a Turing machine into the mechanics of one such system, and you can get a problem where calculating what happens in a finite time requires knowing if said Turing machine halts...) (I would elaborate into a full answer but cannot, due to lack of reputation on this subsite. This site really doesn't care about cross-discipline collaboration...)

@PcMan: Actually single core/thread processing speed HAS pretty well stagnated: https://preshing.com/20120208/a-look-back-at-single-threaded-cpu-performance/  Where you're seeing performance increases is in putting multiple cores in a CPU, and doing instruction-level parallism in the core.  But multiple cores only help if you can parallelize the problem, and there are a great many problems that are inherently sequential.  And you also get to a point where the bottleneck isn't flops, but communication between cores.  (See e.g. GPU programming.)

@jamesqf You know what? you win. I refuse to enter a factual arguement with someone that denies facts. go read about Moore's Law, see if you can find the bit that talks about ""single core processing". I guess you are readibng a different Moore's LAw than I am.

@jamesqf That article is ancient.  IPC has continued to improve quite dramatically.  A 5800X has over double the single thread performance of an i7 970 from a decade ago.

@PcMan: Factual argument?  Your "fact" seems to be more like wishful thinking, expecting that because a certain technology has shown past performance increases, that it will continue to do so indefinitely - something not borne out by either experience or physics.

This is a broad question, hence a broad answer
As high eng CFD now stands, it already is correct enough for, say, 95% of use cases. I am not aware of much utility in modelling complex turbulent flow to a high level of accuracy.
CFD will proceed to become more and more accurate, but 100% accuracy will never be achieved, not at least if we are to assume this would mean a 100% accurate path prediction at molecular / atomic level.
The thing is, even nature can't replicate flow events. Any fluid flow is chaotic, and will only seem steady or repeating if observed at great enough scale. By nature, all flow obeys the principle layed out by Heraclitus:
"You cannot step into the same river twice"

So if throw same stone in glass of calm water from same height,water movement in microscopic level will never be the same?

Exactly. If, and only if you could make every single variable the same, the fluid dynamics of the event might be the same. But even if you do everything the same, the universe will not. On the smallest scale you will have virtual particles that randomly interfere with the experiment, altering the results ever so slightly.

@JurgenM No matter how calm it looks, any two bodies of liquid water are never the same. Each and every one of its molecules is in a different energy state, moving and bouncing with a different angle and velocity. Brownian motion giving rise to an unending number of unpredictable convective flows, and that's even if both those bodies have the same overall temperature. Then when you factor in all the boundary layer interactions, things get much much crazier still...

@Jurgen M: Assuming a glass of water contains one US cup, there are (per Google) 8.3569904e+24 molecules in that glass.  Even if you could somehow get every one of those molecules going in EXACTLY the same random direction & speed in both glasses (which you can't: see the Heisenberg uncertainty principle), there are 3 atoms in each molecule, vibrating and spinning in various modes, some of which are only approximately real (because of quantum :-)), and our friend Chaos (AKA sensitive dependence on initial conditions) will amplify even the tiniest difference.

as for  accuracy - there would be some use cases. Something i could think of, right now - boundary layer separation and detached flows over airfoils (leading to stall), especially to determine the stall and margin in axial compressors. To my knowledge, current CFD isn't really up to the task.

I'm pretty sure stall behaviour of airfoils can be reliably modelled with CFD. How the flow acts after separation can be modelled to a satisfactory level.

100% correct, no.  That's because CFD (and a great many other computer applications) work on numerical approximations.  There's either no exact solution* known, or the exact solution isn't computable. So the application uses numerical approximations, typically on a grid or mesh.  To get a better approximation, you either make the grid smaller, or use a smaller timestep (both of which increase the computation time needed).  But you won't get 100% exact unless you use an infinitely small grid spacing & timestep**, which is impractical.
Another problem is that floating point computations on a computer have only a limited precision. (About 7 decimal digits for single precision, 15 for double.
Also, when you get into turbulent flow regimes, you run into the problem of sensitive dependence on initial conditions, AKA 'chaos" or "the butterfly effect".  Change the input to a problem ever so slightly, and after some time the outputs will be entirely different: https://en.wikipedia.org/wiki/Chaos_theory
*For instance, spacecraft trajectories.  There's no general solution to the 3 body problem - how 3 or more objects move under the influence of gravity.  But numerical approximations are good enough to land a spacecraft at a given spot on Mars, or play gravitational pool among the moons of Jupiter & Saturn.
**Or the Planck length & time, if you accept the theory that spacetime is quantized: https://en.wikipedia.org/wiki/Planck_units  At the current state of computer tech, there's not much practical difference :-)

First, the Millennium Challenge asks about the existence and uniqueness of a solution to the Navier-Stokes (NS) equations given any compatible initial/boundary conditions. This question is of significant interest from an applied mathematics perspective, but it doesn't* help with actually obtaining the numerical solution and, therefore, is of limited interest to engineers.
* But who knows? Maybe a constructive proof will actually aid in solving the equations.
Second, assuming uniqueness and existence hold, Direct Numerical Simulation (DNS) of the NS has been shown to match experiments extremely well where continuum holds. DNS can even substitute experiments in many cases, assuming you can actually get the solution in reasonable time and with existing computational capabilities. The problem lies in completely resolving the length scale of the turbulence, which would require a mesh size that scales with Reynolds number to $Re^3$; the time step size also shrinks as a power of the Reynolds number. For any reasonable engineering problem, the memory/processor/time required to solve is prohibitive for practical purpose.
Hence the reason for turbulence modeling, which makes practical computation tractable. These models ignore the turbulence at small length scales by mimicking their effects on the larger scales in a bid to predict phenomena of interest to engineers, such as drag, flow separation, eddies, etc. However, there is no free lunch; the "truncation" of the length scale means that turbulence is not resolved naturally, but rather "prescribed" via parameters; and you usually don't know what these parameters should be until you've resolved the turbulence.
If that sounds like a chicken and egg question to you, you're right! That's why CFD (with turbulence modeling) still requires experimental verification and will never be 100% correct, as you put it.

No, it will never be 100% accurate. Air or water are quite well described by the Navier-Stokes equations assuming the fluid is a continuum. Usually it is also assumed that they are Newtonian fluid.
The Navier-Stokes equations for a turbulent flow must be solved numerically (for some laminar flows analytical solutions exist). Numerical solutions are never exact for these problems, no matter what kind of order of accuracy you use for your discretizations (FDM, FVM, DG, FEM,...). There will always be some numerical errors (I am now ignoring turbulence modelling, because it is obvious that the closures are always only approximate, the only hope for exact stuff would be in DNS).
Even if you solve the Navier-Stokes solutions exactly (as you can do in some laminar flows), you only solved the model equations. Real fluids are made of molecules, not a continuum. You could do molecular dynamics solution (see https://mattermodeling.stackexchange.com/questions/tagged/molecular-dynamics) but you will again solve some model equations - with some potentials between molecules and atoms. Real molecules are made of nuclei and electrons. The electrons interact in a difficult way and quantum effects will appear. There is inherent randomness in them. Again, models for many particle quantum systems exist - like DFT or H-T, but there are approximations inherent in their formulation.
Less importantly, nuclei are obviously also compounds of nucleons, which are interacting by some complicated potentials through pions, but more exactly actually again made of quarks).
Each of the steps of course require immense computational power even for some small problems, but there are barriers of other kinds in the models themselves that made some aspects essentially random.
And then the whole issues of unknown initial conditions, unknown boundary conditions and deterministic chaos. Those are very important for actual solutions for a given time, less important for time-averaged values.

For the reasons cited above, the answer definitely No, but one point to remember here is that high-end CFD does not have to be perfect to be immensely useful. Imagine one wanted to get 7-place precision out of a temperature prediction in CFD. This would be a fool's errand because in engineering practice, you can't measure free-stream temperatures to that precision in the first place. (It has been said that three-place accuracy was sufficient to design the SR-71.)

There are various CFD methods which all involve some trade-offs between computational complexity and precision. Obviously Direct Numerical Simulation, the computationally most intensive one, is the only method which can be considered for your question - and even in DNS small-scale turbulence is usually parametrized. DNS is already almost prohibitive but going beyond 95% will require exponentially even more resources for every percent.
In fact, I would intuitively say that you would need a computer with processing power matching the number of molecules - which by definition - even if it could really exist at all - is to be at least few times larger than the simulated environment. Then there is of course the Millennium Prize - if there is no such solution, no amount of processing power could get you there.
And do not forget than even very high end DNS can end up with dramatically wrong results if there happens to be a small-scale phenomenon that happens below the resolution of the model - something rare today mostly because we are starting to have very good experience with DNS and most of these are already known.

In DNS small scale turbulence cannot be parametrized, that is the very definition of DNS. The assumptions used are the Navier-Stokes equations and hence continuum and usually a Newtonian fluid is assumed. There is no point speaking about the number of molecules in DNS. If you want molecules ,speak about molecular dynamics, not about DNS.

No simulation, in whatever field, can be 100% correct. Just because computer discretize. And small errors diverge exponentially with time (search for Lyapunov exponent).

It is safe to say that it will never be 100% correct. It would require accounting for and simulating each single fluid molecule. As little as one cubic centimeter of air has more that 10 to the power of 19 molecules: it is more that 10.000.000.000.000.000.000 molecules. Good luck having any existing or future piece of hardware simulate all the interactions beetwen them.

authors: Vladimir F Героям слава


text:
Why did the FAA allow Boeing to self-regulate?
Amidst the Boeing 737 MAX crisis, and finding out after those two fatal crashes that Boeing's 737MAX had been issued self regulation power by the FAA, it has always bothered me, why did the FAA do that in the first place?
I could perfectly understand that the FAA couldn't keep up with the advancement in technologies from aircraft manufacturers, but why give this self-regulatory power? This was clearly a recipe for disaster.
If the FAA couldn't keep up, why not instead pass this regulation approval to a coalition of representatives of multiple organizations like NASA, AIA, AOPA, ICAO, etc.
Even random pertinent staff from other companies could be selected in the same fashion there is jury selection for impartiality.
Giving thoughts to this, I think all aircraft should be approved in this manner in a global participation collaboration, and I think it would achieve faster certification and more perfect aircraft.

This is not really an aviation question. It is a question of engineering (why was this engineering decision made?) and ultimately politics (why does the government not bureaucratically involve itself in every single design decision made everywhere?). To claim that someone, "should've known," about this particular issue is simply hindsight bias. Otherwise, are we going to note the literally thousands of correct non-fatal decisions that Boeing self-regulated?

@StephanSamuel It's not a question about flying airplanes, but it's definitely a question about aviation. It just happens to be about the intersection of aviation, engineering, and politics.

The MAX fiasco wasn't a case of the FAA being behind the technology, or a case of "self regulation" in the sense of Boeing being left completely alone.
It was a case of the relationship between the regulator and OEM becoming a bit too intimate and comfortable, resulting in the FAA accepting a flawed risk/failure effects analysis to justify a system architecture that might not normally get past them. In this particular case the single AOA vane input channel for the MCAS system, justified because the event risk case was piggybacked onto an existing failure mode (stab trim runaway).
In other words, the FAA accepted Boeing's analysis that the existing failure procedures for stab trim runway (only a "major" event classification event IIRC, in the minor/major/hazardous/catastrophic risk assessment structure), and the associated risk category, made the single channel input acceptable from a risk perspective. In the spinning galaxy of technical and political issues revolving around the whole MCAS story, that's the basic root issue when you dig all the way down.
These sorts of problems that come up during certification, and clever bandaid solutions implemented to deal with them, are nothing new. When you see strakes and VGs and vortilons on wings and tails, they are usually band aids to fix a problem that came up unexpectedly during flight testing and avoided a major redesign. MCAS was a bandaid solution using software and some hardware integrated into the stab trim and stall protection system.
Boeing had a wing flutter problem during the 747-8 certification, where unanticipated aerolastic wing flex problems resulted in a low frequency vibration of the entire wing, fixed by the most amazing band-aid I've ever heard of, using the normally dormant fly-by-wire ailerons as active flutter dampers in cruise, almost entirely with software. You can bet there were a lot of reports provided to the FAA to get that certified.
In the case of MCAS, there was a fairly unique set of circumstances, and a system architecture was approved that shouldn't have been, basically because of too much trust, and key individuals dropping the ball.
And this is the conundrum. The regulating agency will grant a certain amount of trust in the OEM, because the staff level would have to triple if the regulator is going to review and challenge every detail of an OEM's design proposal.
Typically senior engineers within the OEM are granted a delegated approval status by the regulator for smaller mods, and they also become the primary engineering interface with the regulator for approval of the major stuff (in Canada they are called Design Approval Delegates, or DADs). Normally there's a reasonable balance struck when all parties are operating in good faith. This was a case where that failed, but it does work reasonably well 99.9% of the time.

People also need to think about the consequences of increasing regulatory time. How much of the cost will come back down to the passengers? The MCAS was bad, but it wasn't a systemic problem. The NASA Challenger o-ring incident though, definitely a systemic problem.

What really got Boeing in trouble was the fact that the flight regime the FAA had agreed to, for the mitigation MCAS was to address, turned out to be more extensive than they'd been told as flight testing progressed, and Program's Exp Test Pilot was charged because of an incriminating email revealing that they intentionally kept the FAA in the dark. The pilot was actually charged criminally, but I believe the case was dropped.

What an odd news article (about the 747-8 fix), because load alleviation through use of the wing devices is pretty common...

@Moo Use of a control surface to actively subdue an elastic vibration mode by actively opposing the vibration with software generated displacements? I've never heard of such a thing before.

@JohnK congratulations, you havent heard of one specific application of using the very same control surfaces to alleviate load and other factors.  IMHO this is akin to putting something new between two slices of bread and then celebrating the fact that you invented the concept of a sandwich.

@Moo Not talking about auto retract of flaps from overspeed or anything like that. I'm talking about using a normally dormant surface to directly oppose and eliminate a wing flex oscillation using software.  If you know of a previous case, I'm all ears.  Or... eyes.

The FAA does not have enough resources to post inspectors to all the situations that require them, so it relies on the concept of delegation through designation to do its job. That ranges from Designated Examiners for people seeking pilot licenses or ratings, to Designated Airworthiness Representatives for issues related to aircraft inspections, etc. It is a normal practice that cannot be replaced by simply swelling the ranks of the FAA with many more employees. In airline manufacturing environments, some employees become the FAA's designated personnel to perform those functions.

This is really the answer to the question. To have the government approve every design decision, you would exactly (not figuratively or nearly) have two design teams simultaneously designing the exact same airplane, one at Boeing and one at the government (or pick-your-favorite-semigovernmental-regulatory-agency).

Boeing isn't just any manufacturer. It's a vital supplier of US DoD. It's essential to the US to have a successful domestic manufacturer for large commercial airframes, not just out of pride, but also to use that expertise for its military needs.
In simple terms, this means Boeing is "too big to fail", it has to stay in business and afloat. This has resulted in some preferential treatment when it came to the MAX case; the company's executives were spared prosecution to avoid disrupting the business.
Multi-agency, and especially multi-national regulations and approvals always take much longer to achieve. One agency is always quicker than two. Zero is even quicker than one. The purpose of regulation isn't to make airplanes as safe as possible - it's to strike a balance between safety and commercial needs.
In Boeing's case, the FAA has allowed this balance to shift a bit towards commerce. Some major decisions that require FAA approval were treated as minor ones that don't. Boeing still follows the same rules as all others, it's just that they get more trust and less micromanagement.

can you explain how Boeing receives preferential treatment on its commercial side due to its relationship on the military side? It seems to be two totally different parts of the government.

When I was thinking about multiagency, it was more in a fashion like setting up a group of qualified persons selected from the areas in question from those agencies, not like the process has to go to agency A, then agency B then C, etc. Then the FAA would set a a standard framework that the group would follow for the certification process.

@Timbo The treatment is more in terms of protecting the company as a whole from commercial trouble, not in special permissions.

Where did the FAA fail?
The catch here is it didn't necessarily fail due to a lack of regulation. Had Boeing made a 7107 (imaginary for the sake of argument) instead of the 737-MAX, it would have required complying with all the regulations the FAA has for a brand new type of airplane. But the 737 is the most popular passenger aircraft in the world (it's been around since 1967!), and is ubiquitous in terms of ecosystem (piloting, maintenance, etc.). Boeing was banking on that when they started the MAX program.

“Our marching orders are no training impact on this airplane. Period,” Richard Reed, a former Federal Aviation Administration engineer, recalled a senior Boeing official telling him during a meeting in the early years of the MAX’s development.

The key piece of the puzzle here is that the FAA has a process where airplane manufacturers and can avoid all sorts of regulatory red tape by making a new model of an already approved airplane. Those compliance costs add up quickly, creating a financial incentive to avoid them. As such, Boeing essentially took a 737 and started massaging it, while catering to the FAA's rules regarding redesign. The best example of this is that the cockpits were virtually identical.

"FAA-approved this for two-and-a-half hours of computer-based training for the transition between the two aircraft," Wilson continued. "All the overhead panel switches are the same. The only minor difference is, because of the change in the display, is to move some of the center console items here on the forward console."

Boeing's decision silo
The failure to regulate MCAS (the system that caused the crashes) was due to a series of seemingly small decisions that lead up to the fatal flaw taking shape. I went into detail on this answer, but the TL;DR is that the MAX changed just a bit too much related to the handling vs previous 737 models. MCAS was designed to make small control changes to smooth those differences out. MCAS would not get any dedicated indicators (as a standard option) for the sake of the "same cockpit" narrative.
Due to a failure of internal Boeing communication, MCAS was made four times more powerful than the original spec, and could activate at lower altitudes. Add in issues with the system that told MCAS what the plane's angle of attack was, and you have a recipe for disaster. Because that was not properly communicated outside the group that made the change (something known as a corporate silo), Boeing scarcely mentioned it and airlines left it out of manuals, meaning few pilots even knew the system existed. The FAA accepted that pilots could use known indicators and procedures (runaway stabilizer) to turn it off in a safe amount of time.
It wasn't until you have two crashes of the same airplane type that this methodology of recertification falls apart. Boeing wasn't required to disclose the existence of MCAS, or what decisions lead to its eventual unsafe state. The FAA noted that in their report (12.2.2 sec 4, emphasis mine)

Based on the JATR team’s observations and findings
related to the FAA type certification process, JATR
team members recommend that the FAA review and
update guidance pertaining to the type certification
process with particular emphasis on early FAA
involvement to ensure the FAA is aware of all design
assumptions, the aircraft design, and all changes to
the design in cases where a changed product
process is used. The FAA should consider adding
feedback paths in the process to ensure that
compliance, system safety, and flight deck/human
factors aspects are considered for the aircraft design
throughout its development and certification.

In short, Boeing didn't "self-regulate", as much as know the existing system well enough to avoid enough questions being asked to catch the MCAS problem before it became deadly.

What do you mean by "redesigned an airplane from the ground up"? It's more like the minimum changes to compete with the A320NEO.

@fooot Good point. Edited.


text:
Why would autopilot be prohibited below 1000 feet AGL?
Came across this airplane on controller. It has a label on the panel that says: "Autopilot prohibited below 1000' AGL".

Why?

(source)

Due to regulatory reasons.
From a purely technical standpoint the autopilot does not care about your height, it works just fine at every altitude (of course the aircraft cannot go above it service ceiling or below ground...).
However, from a regulatory standpoint some APs are only certified for operation above some minimal altitude, e.g. to avoid controlled flight into terrain situations.
Without knowing the exact reasoning of this AP, reasons can involve:

The AP cannot guarantee that its engagement will not let the aircraft sink for a couple of 100 ft before recovering. With safety margin this zone extends 1000 ft
The AP does not feature a ground altimeter. Therefore it does not know how high above ground it is, therefore it cannot adapt its behavior close to ground. This does not fulfill the safety requirements, therefore this limit.
If the AP encounters a fault, the pilot shall be granted enough time to take over control. For example, if the autopilot does not feature enough redundancy to guarantee that it performs with acceptable risk under all possible fault cases, the AP is simply restricted to a minimum altitude. This way, the pilot can take over control when the AP fails and still has enough altitude to recover the aircraft.

Certification is expensive, therefore such trade offs in operational limits are often accepted in aviation products to keep the cost low.

Also technical reason: on low altitude there are buildings and other features which may interfere with AP (multipath signals). Near airports there are checks and warning (e.g. La Guardia), but nobody can test everywhere (which would require a lot of low altitude flights, at different low altitude, different directions, etc.).

"it works just fine at every altitude" If the control loops haven't been tuned for flight in ground effect, it's going to have problems.

FAA Advisory Circular AC 23-17C describes procedures and requirements for certifying aircraft under part 23.
The autopilot section, (23.1329, starting on page 250) says in part:

A single malfunction may not result in a hardover signal in more than one axis.

And:

The results of malfunction testing determine which flight condition is
most critical. The effects of autopilot runaways are more pronounced
at aft CG. Also, the phase of flight with the largest contribution to
adverse conditions varies with airplane model.

Typically the most critical flight condition would be in approach configuration down low, and a erroneous full nose-down command from the autopilot.  This condition is tested, (starting out at higher altitudes and incrementally stepping down...) at both forward and aft CG limitations.
A recognition/reaction delay from the pilot is considered, and the altitude lost in recovery is noted.  From there an appropriate safety margin is calculated to establish the no-lower-than limitation.


text:
Why are cockpit instruments white on black dials?
Which is easier to read:  white on a black dial or black on a white dial? It would seem most aviation instruments are white on black.

On some other stack (overflow? Superuser?) There is a question about the "perfect" colour screen for coding on a computer. This might give some related insights since the majority seem to prefer dark background for various reasons

For night flying the white on black scheme emits probably 1 or 2% of the light that a black on white display does. This will make a very significant difference in cockpit light levels and night vision.
While lighting levels could be turned down on the black on white displays the contrast would suffer. With white on black the lighting levels can be left relatively high, the contrast will be improved and pupil contraction will be less when looking at the instruments.

Yes, and imagine the fun if they used black on white for Head's Up Displays.

Besides having a bright white light shine at you at night makes it next to impossible to see anything on the outside of the plane, it also will tire you out much faster looking at bright instruments all the time. (Speaking as a programmer, I can work longer and focus a lot better with a dark color scheme on the screens than with a light one).

You also need a lot less fluorescent paint to make the numbers and needle light-colored.

And a lot of people died for that fluorescent paint back in the day

@Adwaenyth: related: Why is there no dark theme on SO? (there are 3rd-party dark themes, but like most web pages, SO by default uses black on white so it hurts your eyes to tab to a web browser away from terminal windows and editors.)

@PeterCordes I'm a programmer, not a SE programmer. Don't know why no one made a dark theme for SE yet. However I do think you're usually not hours a day browsing on SE with no break in between.

@PeterCordes everything on my screen is black-on-white so I have no problem with it. I think the problem is the contrast between bright and dark themes/objects, not specifically one or the other. I find dark themes work well in a dark environment too.

@immibis: I don't like having my room very brightly-lit, so large areas of white on a nice monitor that's not mis-calibrated to make white into beige or something is hard on the eyes.  If you do like bright themes in general, then of course you won't have a problem with SO or most web pages.

Sounds like a poor lighting setup then... if it's too bright at night, use less-bright bulbs, if it's too bright in the day, close your blinds or curtains partially, if your monitor is too bright then turn the brightness down.

@Adwaenyth: I was linking that Q&A because of the interesting answers that already exist, not because I expected you to answer it.  This Q&A inspired me to give the Dark Reader extension for Chrome a try.  It invents dark themes on the fly for every web page.  Its "Dynamic" setting works ok for SO.  Filter+ looked even better, but locked up the Intel Linux graphics drivers for Skylake's onboard GPU after several hours, when clicking a link >.<

@immibis: Using dark themes is a valid choice.  I don't want to mess up my monitor settings just to make bright themes less bad for text in my preferred room lighting, and then have to fix it for watching movies or playing games.